1. Field of the Invention
The present invention relates to extrusion apparatus for softening plastics materials so that they can be extruded through an extrusion die to provide an extruded shape of predetermined cross-sectional configuration. More particularly, the present invention relates to extrusion apparatus in which a pair of individual extruders is provided, each extruder feeding material into a single extrusion die for coextrusion of plastics materials from two separate sources, wherein one of the extruders is supported above the other, to feed a common extrusion die, and the longitudinal axes of the respective extruders are disposed at an acute angle relative to each other.
2. Description of the Related Art
The coextrusion of materials from plural extruders is known. For example, in U.S. Pat. No. 3,780,154, which issued Dec. 18, 1973, to Karl Heinz Muller et al., there is disclosed a pair of extruders for feeding a single extrusion die and for extruding a cylinder from a first material and simultaneously extruding over and surrounding the cylinder an outer sleeve from a different material. The extruders are so oriented that the center cylindrical portion of the extruded article is formed from material that issues from a horizontally arranged extruder, while the surrounding sleeve material is provided by a second extruder that is positioned so that its longitudinal axis intersects and forms an obtuse angle with the longitudinal axis of the first extruder. The relative positions of the two extruders, and their orientation, are fixed.
Another patent that discloses coextrusion of materials using a plurality of extruders to feed a single extrusion die is U.S. Pat. No. 4,643,659, which issued Feb. 17, 1987, to Helmut Paul. Three separate extruders are disclosed, one of which is mounted on an inclined frame and is movable along the inclined portion of the frame toward and away from an extrusion die to which the remaining two extruders are operatively connected.
In the course of operating extruders, it is at times necessary to remove the extruder screws, either to permit repair of the original screws, or to permit substitution of different screws. In the known coextrusion arrangements disclosed in the above-identified patents, removal of the screws from the non-horizontally positioned extruders is rendered difficult. In each instance, withdrawal of the screws from the inclined extruder must be accomplished either through the rear of the barrel, or in the case of the structure disclosed in the Paul '659 patent referred to above, the inclined extruder must be withdrawn from the die and moved upwardly along the inclined track to permit screw removal to be accomplished through the forward end of the barrel. In each instance, the disclosed arrangements do not permit convenient removal of the screws.
Additionally, even with the Paul '659 structure, which would permit removal through the forward end of the barrel of screws having constant screw diameters, if a twin screw extruder were to be provided having conically shaped screws, those whose outer diameter diminishes from the rear to the forward end of the screw, removal of such screws would have to be accomplished through the back end of the barrel which would be difficult and inconvenient.
Each of the above-identified patents also shows the inclined extruder to be positioned so that its axis defines an obtuse angle with the axis of an opposed, horizontally oriented extruder. Consequently, considerable additional floor space is required in order to accommodate such an arrangement of extruders, which severely limits the number of coextrusion arrangements that can be accommodated in the floor area of a given manufacturing facility.
It is an object of the present invention to overcome the problems and limitations that are inherent in the prior art structures as disclosed in the above-identified patents.
It is a further object of the present invention to provide an improved coextrusion system for more convenient removal of the screws from an upwardly extending extruder, and also for minimizing the floor area required for such a coextrusion system.